Okay, Guy; you've eliminated wiring as the problem. The possibility that one of the back surround speakers is defective still remains. As was said before, you should temporarily connect other speakers to the back surround terminals to check this before you return the receiver.

If it becomes necessary, there are several fine receivers available for well under $2,000, especially the Denon and Onkyo models.

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Enjoy the music, not the equipment.